Associative recall is a process by which a presented image, i.e. a cue, triggers a reactivation of the internal representation of an associated image. The associated “image” may be in any sense modality or more abstract, and it may be triggered by external sensory information or internal broadcast. Since by this process a presented image evokes a memory of what has accompanied it before, associative recall can be intertwined with prediction, and hence the automatic transformation of sensory input into motor output.
However, a difficulty in implementation of associative recall in neural systems, whether artificial or biological, arises due to a common aspect of the initial encoding of external objects by biological sensory arrays: the initial encoding of an object (whether it be a smell or visual image) by simple “feature sensors” often entails considerable overlap between the patterns encoding fundamentally different objects. Thus the presentation of an apple or a rock of similar size and shape may trigger very similar patterns of initial activation in the retina and in the primary visual sensory area, and yet of course require very different motor reactions. Similarly, the pattern of activation in the olfactory epithelium and in the olfactory bulb evoked by two distinct odorants which differ by a single molecular motif will considerably overlap, and yet can be associated with two substances of different import, one edible the other poisonous.